Page History

...

/* sock is a connected TCP socket */

uint32_t num;

if (recv(sock, (void *)&num, sizeof(uint32_t), 0) < 0(int)sizeof(uint32_t)) {
  /* Handle error */
}

printf("We received %u from the network!\n", (unsigned int)num);

This program prints out the number received from the socket using an incorrect byte ordering. For example, if the value 4 is sent from a big endian machine, and the receiving system is little endian, the value 536,870,912 is read. This problem can be corrected by sending and receiving using network byte ordering.

Compliant

...

Solution

In this compliant code examplesolution, the programmer uses the ntohl() function to convert the integer from network byte order to host byte ordering:

/* sock is a connected TCP socket */

uint32_t num;

if (recv(sock, (void *)&num, sizeof(uint32_t), 0) < 0(int)sizeof(uint32_t)) {
  /* Handle error */
}

num = ntohl(num);
printf("We recieved %u from the network!\n", (unsigned int)num);

...

If the programmer is careless, this bug is likely. However, it will immediately break the program by printing the incorrect result and therefore should be caught by the programmer during the early stages of debugging and testing. Recognizing a value as in reversed byte ordering, however, can be difficult depending on the type and magnitude of the data.

Automated Detection

Bibliography

...

...

Image Modified Image Modified Image Modified